Highly efficient recovery of propane by mixed‐matrix membrane via embedding functionalized graphene oxide nanosheets into polydimethylsiloxane

To construct rapid C₃H₈ transport pathways in polymer matrix, alkyl chain‐functionalized graphene oxide (GO) was prepared via grafting octadecylamine (ODA) molecules and then embedded into polydimethylsiloxane (PDMS) matrix to obtain high‐efficiency mixed matrix membranes (MMMs). The incorporation of alkyl chains contributes to lowering the surface energy of GO nanosheets and providing higher affinity with PDMS matrix. Additionally, the alkyl chains on the surface of ODA‐functionalized GO nanosheets (ODA‐GO) are in favor of C₃H₈ adsorption, thus conferring continuous and specific transport pathways for C₃H₈. The optimized membrane with ODA‐GO loading of 0.3 wt% exhibits the C₃H₈ permeance of 1897 GPU and the C₃H₈/N₂ ideal selectivity of 67, which are 50.2 and 72.5% higher than those of bare PDMS membrane, respectively. The simultaneous enhancement of C₃H₈ permeance and C₃H₈/N₂ ideal selectivity indicates that ODA‐GO is an effective filler applied in MMMs for C₃H₈ recovery. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3501–3510, 2017     

Study on CO2 facilitated separation of mixed matrix membranes containing surface modified MWCNTs

Mixed matrix membranes (MMMs) for CO₂-facilitated separation were prepared by incorporating different surface-modified multiwalled carbon nanotubes (MWCNTs) in a fixed carrier membrane material. Polymer containing amino groups, poly(vinylalcohol-co-vinylamine) (VA-co-VAm) was synthesized as polymeric matrix. MWCNTs as well as MWCNTs surface-modified with  OH and  NH₂ were applied as nanofillers. The physical property, chemical structure, and membrane morphology were characterized by FT-IR, TG, XRD, DSC, CA, XPS, and SEM. The effects of content, functional group, temperature, and pressure on gas permselectivity were studied. Results show that the incorporation of nanofillers can effectively restrict the polymer chain packing and lead to low crystallinity. The MMMs exhibited higher CO₂ permselectivity than the pure polymeric membrane. For all the MMMs, the CO₂ permeance and selectivity increased with MWCNTs contents to a maximum and then decreased. MWCNT-NH₂ can be regarded as the most effective nanofiller. MMMs with 2.0 wt % MWCNT-NH₂ displayed the highest CO₂ permeance of 132 GPU and CO₂/N₂ selectivity of 74. Both CO₂ permeance and selectivity were decreased with feed gas pressure and temperature. The membrane exhibited good stability in the testing with the binary gas mixtures of CO₂/N₂ for 110 h under 0.54 MPa. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47848.     

Fabrication and characterization of PDMS coated PES membranes for separation of ethylene from nitrogen

Composite membranes were prepared for separation of ethylene from nitrogen using polyethersulfone (PES) as support and polydimethylsiloxane (PDMS-a grade of silicone rubber) as active layer at various concentrations. Permeance and ideal selectivity were measured for all membranes under the transmembrane pressure of 2 to 6 bars. Influences of affecting parameters on membrane performance (i.e. permeance and selectivity) were investigated. The studied parameters include: PES concentration in casting solution, solvent type, PDMS concentration in coating layer, support thickness, coating thickness and coagulation atmosphere. For all coated membranes, the ethylene permeance was higher compared to the nitrogen permeance except for 5% coated air coagulated membrane. This membrane was more permeable for N₂ in comparison with ethylene under the pressures higher than 2 bars. The nitrogen permeance exhibited a rather constant value. There was no significant change in nitrogen permeance with respect to the coating layer, whereas ethylene permeance was highly influenced by coating layer composition and support thickness. The governing mechanism for the separation is solution-diffusion of ethylene in PDMS layer (solution-diffusion model). The SEM study was carried out for investigation of membrane morphology. In a run ethylene was passed through the membrane after the passage of nitrogen. In the second run ethylene was passed through the membrane before nitrogen. The nitrogen selectivity was reduced in the later test. This is due to the ethylene high solubility in membrane matrix.     

Preparation and characterization of polysulfone mixed matrix membrane incorporated with palladium nanoparticles in the inversed microemulsion for hydrogen separation

Polysulfone (PSf) membrane shows acceptable gas separation performance, but its application is limited by the “trade-off” between selectivity and permeability. In this study, PSf mixed matrix membranes (MMMs) incorporated with palladium (Pd) nanoparticles in the inversed microemulsion were proposed for hydrogen (H₂) separation. Pd nanoparticles can be kinetically stabilized and dispersed using electrostatic and/or steric forces of a stabilizer which is typically introduced during the formation of Pd nanoparticles in the inversed microemulsion. Pd nanoparticles were synthesized by loading (PdCl₂) into the polymeric matrix, polyethylene glycol (PEG) which acts as reducing agent and stabilizer. The dry–wet phase inversion method was applied for the preparation of asymmetric PSf MMMs. The effects of Pd (0–4 wt%) on the membrane characteristics and separation performance were studied. Experimental findings verified that the MMMs are able to achieved a high H₂/N₂ selectivity of 21.69 and a satisfactory H₂ permeance of 46.24 GPU due to the changes in membrane structure from fully developed finger-like structure to closed cell structure besides the growth of dense layer. However, the selectivity of H₂/CO₂ decreased due to the addition of PEG.     

Gas transport behavior of DMDCS modified MCM-48/polysulfone mixed matrix membrane coated by PDMS

Mesoporous MCM-48 silica was synthesized by templating method and the structure of particles was characterized by XRD, TEM and N₂ adsorption techniques. The surface modification of particles in order for introducing into PSF matrix was performed by dimethyldichlorosilane (DMDCS) silylation agent. SEM images of as-synthesized and modified MCM-48/PSF MMMs indicate that in the modified MCM-48 silica particles adhered well to the PSF matrix and that the synthesized MMMs were defect free. The incorporation of MCM-48 particles in to the PSF matrix and also surface coating of these MMMs by polydimethylsiloxane (PDMS) were performed. The quality of surface coating was investigated by SEM images and permeability tests. For all gases tested (N₂, CO₂, CH₄ and O₂), the permeabilities increased in proportion to the weight percent of MCM-48 present in the film and the calculated CO₂/CH₄ and O₂/N₂ selectivities of PDMS coated membranes showed enhancement in ideal and actual selectivities both.     

Nano-silica/polysulfone asymmetric mixed-matrix membranes (MMMs) with high CO2 permeance in the application of CO2/N2 separation

Nano-sized silica/polysulfone (PSf) flat sheet asymmetric MMMs with high CO₂ permeance for CO₂/N₂ separation were fabricated by dry/wet phase inversion method using N, N-dimethylacetamide (DMAc) and tetrahydrofuran (THF) as solvents and ethanol as additives. The results indicated that the addition of nano-silica on the polymer matrix resulted on reduced membrane performance due to void formation and particle agglomeration. Optimum membrane performance was obtained at the following fabrication parameters: 22 wt.% PSf, 31.8 wt.% DMAc, 31.8 wt.% THF, 14.4 wt.% ethanol, 20 s evaporation time, and 0 wt.% silica loading, with CO₂/N₂ selectivity of 15.6 and CO₂ permeance of 14.2 GPU.     

Fabrication and characterization of silica modified polyimide–zeolite mixed matrix membranes for gas separation properties

In this study, new monomers having silica groups were synthesized as an intermediate for the preparation of poly(imide siloxane)-zeolite 4A and 13X mixed matrix membranes (MMMs). The effects of membrane preparation steps, zeolite loading, precursor’s composition, and pore size of zeolite on the gas separation performance of these mixed matrix membranes were studied. The new diamine monomer was prepared from 3,5-diaminobenzoic acid (3,5-DABA), 3-aminopropyltrimethoxysilane (3-APTMS), and zeolite 4A and zeolite 13X in N-methyl-2-pyrollidone (NMP) at 180 °C. Poly(imide siloxane)-zeolite 4A and 13X MMMs were synthesized from pyromellitic dianhydride (PMDA) and 4,4-oxydianiline (ODA) in NMP using a two-step thermal imidization. SEM images of the MMMs show the interface between polymer and zeolite phases getting closer when surface modified zeolite is used. The increase in glass transition temperature (T _g) confirms the polymer chain becoming more rigid induced by the presence of zeolite. The experimental results indicated that a higher zeolite loading resulted in a decrease in gas permeability and an increase in gas pair selectivity. In terms of O₂ and N₂ permeance and ideal selectivity, the separation performances of poly(imide siloxane)-zeolite MMMs were related to the zeolite type and zeolite pore dimension.     

High gas permselectivity in ZIF-302/polyimide self-consistent mixed-matrix membrane

Zeolitic imidazolate framework-302 (ZIF-302) was incorporated within a polyimide (PI) matrix in order to develop a highly selective and permeable mixed-matrix membrane (MMM) for gas separation processes. On the basis of varying fabrication procedures, two different MMMs were formed: a dense MMM (ZIF-302/d-PI) and a spongy, self-consistent MMM (ZIF-302/s-PI). The spongy membrane was shown to have self-consistent and disconnected pores with a reduction in overall membrane density. For ZIF-302/d-PI, a 1.2–1.5-fold increase in the permeability of H₂, O₂, N₂, CO₂, and CH₄ was observed when compared with the pure d-PI membrane. For ZIF-302/s-PI, even better improvements (up to 19-fold higher) in permeance were achieved with negligible effects on selectivity. The gas transport mechanism was then analyzed and showed a considerable enhancement of diffusion coefficients for ZIF-302/s-PI, while ideal gas pair selectivities for CO₂/N₂, H₂/CH₄, and H₂/N₂ were found to be 24.8, 42.3, and 62.6, respectively. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48513.     

Dimethyl silane-modified silica in polydimethylsiloxane as gas permeation mixed matrix membrane

The gas transport behaviors of O₂, N₂, CO₂ and CH₄ were investigated in mixed matrix membranes (MMMs) prepared from polydimethylsiloxane (PDMS) filled with surface functionalized silica (SiO₂) nanoparticles. SiO₂ surface modification was performed through silanization using chlorodimethyl silane. FTIR confirmed the presence of dimethyl silane on SiO₂ (Si-DMS) whereas elemental analysis showed 94.2% successful modification. Thermal gravimetric analysis revealed the improved thermal stabilities of PDMS MMMs. Field emission scanning electron microscopy revealed the uniform distribution of Si-DMS within the membrane. The effect of Si-DMS in gas permeabilities (P) was in contrast to the Maxwell model prediction. Enhanced P values of all gases in PDMS MMMs (as compared to pure PDMS) were associated to the improvement in diffusion coefficients (D_m) despite the reduction in gas solubility coefficients. The increase in D_m values was attributed to the higher free volumes in PDMS MMMs. However, slight declines (<8% of pure PDMS) in selectivities were observed. Overall, PDMS MMMs have improved performances due to enhanced gas permeabilities.     

Study of morphology and gas separation properties of polysulfone/titanium dioxide mixed matrix membranes

Polysulfone (PSf)‐based mixed matrix membranes (MMMs) with the incorporation of titanium dioxide (TiO₂) nanoparticles were prepared. Distribution and agglomeration of TiO₂ in polymer matrix and also surface of membranes were observed by scanning electron microscopy, transmission electron microscopy, and energy dispersive X‐ray. Variation in surface roughness of MMMs with different TiO₂ loadings was analyzed by atomic force microscopy. Physical properties of membranes before and after cross‐linking were identified through thermal gravimetric analysis. At low TiO₂ loadings (≤3 wt%), both CO₂ and CH₄ permeabilities decreased and consequently gas selectivity improved and reached to 36.5 at 3 bar pressure. Interestingly, PSf/TiO₂ 3 wt% membrane did not allow to CH₄ molecules to pass through the membrane and this sample just had CO₂ permeability at 1 bar pressure. Gas permeability increased considerably at high filler contents (≥5 wt%) and CO₂ permeance reached to 37.7 GPU for PSf/TiO₂ 7 wt% at 7 bar pressure. It was detected that, critical nanoparticle aggregation has occurred at higher filler loadings (≥5 wt%), which contributed to formation of macrovoids and defects in MMMs. Accordingly, MMMs with higher gas permeance and lower gas selectivity were prepared in higher TiO₂ contents (≥5 wt%). POLYM. ENG. SCI., 55:367–374, 2015. © 2014 Society of Plastics Engineers     

Synthesis,characterization, and gas separation performances of polysulfone and cellulose acetate-based mixed matrix membranes

ABSTRACT

The combination of polymeric and inorganic fillers inside mixed matrix membranes (MMMs) becomes a hot research topic due to the gas permeability-selectivity trade-off in polymeric membranes. Until recently, the problem of voids hampers the real application of MMMs, hence deep understanding on polymer-particle compatibility is required. This study focuses on the synthesis and characterization of polysulfone and cellulose acetate-based MMMs that combined with ZIF-8 and TiO₂ particles. ZIF-8 dispersed more uniform than TiO₂. The crystallinity of MMMs was higher than pure polymeric membrane. In addition, micro voids in MMMs resulted a slight decrease in CO₂/N₂ selectivity (from 15 to 12).     

Fabrication of Homogenous Polymer‐Zeolite Nanocomposites as Mixed‐Matrix Membranes for Gas Separation

Interfacial void‐free mixed‐matrix membranes (MMMs) of polyimide (PI)/zeolite were developed using 13X and Linde type A nano‐zeolites and tested for gas separation purposes. Fabrication of a void‐free polymer‐zeolite interface was verified by the decreasing permeability developed by the MMMs for the examined gases, in comparison to the pure PI membrane. The molecular sieving effect introduced by zeolite 13X improved the CO₂/N₂ and CO₂/CH₄ selectivity of the MMMs. Separation tests indicated that the manufactured nanocomposite membrane with 30 % loading of 13X had the highest permselectivity for the gas pairs CO₂/CH₄ and CO₂/N₂ at the three examined feed pressures of 4, 8 and 12 atm.     

Effects of THF as cosolvent in the preparation of polydimethylsiloxane/polyethersulfone membrane for gas separation

Polydimethylsiloxane/polyethersulfone (PDMS/PES) asymmetric membranes are widely applied in gas separation. However, the effects of common cosolvent on these membranes remain unknown. In order to study the changes in membrane morphology and gas separation properties, asymmetric PDMS/PES membranes were prepared. The studied parameters were types of cosolvents, tetrahydrofuran (THF) concentration, evaporation time, and PDMS concentration. Membrane morphology was examined using scanning electron microscopy and gas separation was conducted using pure CO₂, N₂, CH₄, and Hat 25°C. The addition of cosolvent into the polymer solution decreased the dope viscosity and delayed liquid–liquid demixing during phase inversion. Macrovoids formation was observed in substructure layer after adding THF and these macrovoids elongated with the reduction in THF content. There were microvoids formed on top of macrovoids and microvoids layer became thicker due to the increasing evaporation time of solvents before coagulation in nonsolvent. The PDMS coating on the PES membrane formed a dense skin layer and exhibited higher selectivity compared to the uncoated membrane. Membrane contained THF cosolvent with 60 s evaporation time and 3 wt% coated PDMS is the optimum membrane among other membranes in this work. The CO₂/N₂ selectivity was enhanced by 73.3% with CO₂ permeance of 44.86 GPU. POLYM. ENG. SCI., 54:2177–2186, 2014. © 2013 Society of Plastics Engineers     

Effect of Dispersed Multi-Walled Carbon Nanotubes on Mixed Matrix Membrane for O2/N2 Separation

Mixed matrix membranes (MMMs) consisting of multiwalled carbon nanotubes (MWCNTs) embedded within polyetherimide were prepared. Surfactants of different charges were utilized to disperse the nanotubes through a simple non-covalent approach. The characterization results suggest that proper selection of the dispersing agent contributed to better dispersion of nanotubes. The MMMs exhibited improved thermal stability and mechanical strength, which indicate the improvement of dispersion and compatibility within the polymer matrix. The resulting membrane exhibited permeance improvement of O₂ and N₂ as much as 87.7% and 120% respectively compared to that of neat polyetherimide. The results implied that Triton-X100 treated MWCNTs is a promising filler to enhance gas permeability.     

Preparation and characterization of polyvinylchloride based mixed matrix membrane filled with multi walled carbon nano tubes for carbon dioxide separation

Poly vinyl chloride/multi wall carbon nano tubes (PVC/MWCNTs) mixed matrix membranes (MMMs) were prepared for gas separation. Raw and functionalized MWCNTs (R-MWCNTs and C-MWCNTs) were utilized in membranes preparation. The C-MWCNT shows better performance compared to raw ones. Membrane (CO₂/CH₄) selectivity was increased from 39.21 to 52.18 at 2 bar pressure by MWCNT loading ratio. The modified membranes with styrene butadiene rubber (SBR-MMMs) showed 63.52 and 34.70 selectivity for (CO₂/CH₄) and (CO₂/N₂) at 2 bar pressure. Mechanical properties analysis exhibited tensile module improvement utilizing blending modification. Increase of feed pressure led to membrane gas permeability decreasing. But gas pair selectivity follows a nearly constant behavior for MMMs and increasing behavior for blend MMMs.     

Preparation and Characterization of Polycarbonate-Blend-Raw/Functionalized Multi-Walled Carbon Nano Tubes Mixed Matrix Membrane for CO2 Separation

Membrane composed of PC as base of polymer matrix with different ratio of multiwall carbon nano tubes (MWCNTs) as nanofillers and poly ethylene glycol (PEG) as second polymer was prepared by solution casting method. Both raw-MWCNTs (R-MWCNTs) and functionalized carboxyle-MWCNTs (C-MWCNTs) were used in membrane preparation. The MWCNTs loading ratio and pressure effects on the gas transport properties of membranes were examined in relation to pure He, N₂, CH₄, and CO₂ gases. Results showed that the use of C-MWCNT instead of R-MWCNTs in mixed matrix membranes (MMMs) fabrication with base of PC provides better performance and also it increases (CO₂/CH₄) and (CO₂/N₂) selectivities to 27.38 and 25.42 from 25.45 and 19.24, respectively (at 5 wt% of MWCNTs). PEG as the second rubbery polymer was utilized to improve the separation performance and mechanical properties. In blend MMMs, highest (CO₂/CH₄) selectivity at 2 bar pressure increased to 35.64 for PC/PEG/C-MWCNT blend MMMs which was 27.28 for PC/MWCNTs MMMs at 10 wt%. Increase of feed pressure led to gas permeability and gas pair selectivity improvement in approximately all of membranes. Analysis of mechanical properties showed improvement in tensile modules with the increase of MWCNTs loading ratio and use of PEG in prepared MMMs.     

Synthesis and gas permeation properties of a single layer PDMS membrane

In this work, a new polydimethylsiloxane (PDMS) membrane was synthesized and its sorption, diffusion, and permeation properties were investigated using H₂, N₂, O₂, CH₄, CO₂, and C₃H₈ as a function of pressure at 35°C. PDMS, as a rubbery membrane, was confirmed to be more permeable to more condensable gases such as C₃H₈. The synthesized PDMS membrane showed much better gas permeation performance than others reported in the literature. Based on the sorption data of this study and other researchers' works, some valuable parameters such as Flory‐Huggins (FH) interaction parameters, χ, etc., were calculated and discussed. The concentration‐averaged FH interaction parameters of H₂, N₂, O₂, CH₄, CO₂, and C₃H₈ in the synthesized PDMS membrane were estimated to be 2.196, 0.678, 0.165, 0.139, 0.418, and 0.247, respectively. Chemical similarity of O₂, CH₄, and C₃H₈ with backbone structure of PDMS led to lower χ values or more favorable interactions with polymer matrix, particularly for CH₄. Regular solution theory was applied to verify correctness of evaluated interaction parameters. Local effective diffusion coefficient of C₃H₈ and CO₂ increased with increasing penetrant concentration, which indicated the plasticization effect of these gases over the range of penetrant concentration studied. According to high C₃H₈/gas ideal selectivity values, the synthesized PDMS membrane is recommended as an efficient membrane for the separation of organic vapors from noncondensable gases. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Enhanced CO2 separation performance of mixed matrix membrane by incorporating amine-functionalized silica filler

Mixed matrix membranes (MMMs) owing to the tunable characteristics and functionalization ability can effectively substitute the highly intensive conventional membranes for industrial-scale CO₂ separation. Further, to strengthen the interfacial polymer-filler interaction, an interfacial design strategy incorporating active functional groups in the filler surface can be demonstrated. In this study, as-synthesized silica nanoparticles (SNPs) was surface functionalized by (3-aminopropyl) trimethoxysilane silica modifier (AFSNP). The CO₂ separation of poly (vinyl alcohol)/polyethylene glycol based MMM infused with surface-functionalized SNP (AFSNP) was conducted. The comparative study highlighted in-depth analysis of intrinsic physicochemical properties of as-synthesized membranes and nanoparticles. Detailed characterization such as advanced microscopic analysis, X-ray photoelectron spectroscopy (XPS) analysis and ninhydrin assay validated the successful grafting of amino groups onto the silica surface. The morphological inspection corroborated the consistent dispersion ability of the nanoparticles in the membrane matrix. The effect of the operating conditions on the membrane selectivity and CO₂ permeance were statistically analyzed by ANOVA. The CO₂ permeation result (CO₂ permeance and CO₂/N₂ selectivity) exhibited many fold increment with surface functionalization of SNPs compared to undoped silica MMM. The defect-free, performance-oriented CO₂-selective membrane thus opened up the possibility of this combination as a prospective contender for large-scale carbon capture studies.     

Asymmetric oxygen-functionalized carbon nanotubes dispersed in polysulfone for CO2 separation

Carbon dioxide separation from flue gases is an important challenge to be faced. Membrane processes are a promising alternative to increase technical and economical constraints once the development of materials with superior characteristics are attained. Integrally asymmetric mixed matrix membranes (MMMs) were prepared by dry/wet phase inversion process of polysulfone (PSF) containing oxygen-functionalized multiwalled carbon nanotubes (MWNT-O). Fourier transform infrared (FTIR) spectroscopy confirmed the presence of MWNT-O in MMMs. Thermal gravimetric analysis (TGA) showed that MMMs are stable up to 150°C. Photomicrographs from scanning electron microscopy (SEM) revealed that MMMs consist of an asymmetric structure with a skin layer supported on a sponge-like substructure. The pore size of the support of MMMs increased with MWNT-O content from 0.4 to 0.8 wt.% and the thickness of the dense layer decreased. However, when the content of MWNT-O increased to 1 wt.%, the pore size decreased, and the dense layer increased. Therefore, MMMs changed CO₂ separation performance. For 1 wt.% MWNT-O loading compared to the neat polymer, CO₂ permeance and CO₂/N₂ selectivity was increased from 1.5 to 2.7 GPU, and from 9.5 to 14.3, respectively.     

High speed spin coating in fabrication of Pebax 1657 based mixed matrix membrane filled with ultra-porous ZIF-8 particles for CO<Subscript>2</Subscript>/CH<Subscript>4</Subscript> separation

Modified ultra-porous ZIF-8 particles were used to prepare novel ZIF-8/Pebax 1657 mixed matrix membranes (MMMs) on PES support for separation of CO₂ from CH₄ using spin coating method. TEM and SEM were used to characterize modified ZIF-8 particles. SEM was also used to investigate the morphology of synthesized MMMs. The MMMs with thinner selective layer showed higher CO₂ permeability and lower CO₂/CH₄ selectivity in permeation tests compared to MMMs with thicker selective layer. The plasticization was recognized as the main reason for rise in CO₂ permeability and drop in CO₂/CH₄ selectivity of thinner MMMs. The gas sorption results showed that the high permeability of CO₂ in MMMs is mainly due to the high solubility of this gas in MMMs, leading to high CO₂/CH₄ solubility selectivity for MMMs. The fractional free volume and void volume fraction of MMMs increased as the thickness of membrane decreased. Applying higher mixed feed pressures and permeation tests temperatures resulted in increase in CO₂ permeability and decrease in CO₂/CH₄ selectivity. At highest testing temperature (60 °C), the CO₂ permeability of synthesized MMMs with thinner selective layer remarkably increased.